>>1
http://common-lisp.net/project/commonqt/ not the lispiest one, but it beats having to write your own interface in C and linking to it
http://common-lisp.net/project/mcclim/ If you liked the Lisp Machine interface, CLIM is awesome, but it's not too well supported on Windows (there are multiple backeds for win32)
For Win32, the commercial vendors do provide their own GUI tools, so if you want easy-to-make ones for Win32, that's also a good bet. (LispWorks, AllegroCL).
http://common-lisp.net/project/cello/ OpenGL and Cells based
http://common-lisp.net/project/cl-gtk2/ GTK for CL (There's multiple GTK implementations for CL, but I can't remember the name of them all, one was lispy, the other meant you wrote)
http://marijn.haverbeke.nl/cl-tk/ There's multiple Tcl/Tk bridge implementations for CL, but I can't remember the name of them all, one was lispy, the other was pretty low-level.
http://weitz.de/rdnzl/ If you like making your interface in .NET
If you like to use X/CLX:
http://www.cliki.net/CLX
http://www.cliki.net/Garnet
http://www.cliki.net/CLUE
http://www.cliki.net/CLIO
http://www.wxcl-project.org/language/en/ wxWidgets based GUI, fairly portable
http://common-lisp.net/project/graphic-forms/ Thin native Win32 GUI interface
There's many others I can't recall right now, but you have a lot of choices, some are mature, others are not that good, some are portable and more bloated, others are thin and low-level, others are platform specific, and some are free, others commercial.
As usual with CL, you have a wide variety of choices of implementations, choose well
!